1. Field of the Invention
The present invention relates to a transmitter, a remote controller and a transmission method.
2. Description of the Related Art
Recently, many wireless communication systems share frequency resource. The frequency resource is divided into frequency bands. Each frequency band is used by a wireless communication system. In each wireless communication system, a signal including an out-of-band component is transmitted. The out-of-band component gives an interference to other wireless communication systems. To avoid giving interference to other wireless communication systems, a guard band is inserted between the frequency bands. When the out-of-band component is wide, a wide guard band is required.
The wide guard band causes a degradation of a frequency efficiency. Therefore, the guard band is better to be as narrow as possible. However, if the guard band gets narrower, it is higher possibility that the out-of-band component exceeds the guard band. The out-of-band component which exceeds the guard band may give the interference to other wireless communication system.
To eliminate the out-of-band component which exceeds the guard band, a BPF (Band-Pass Filter) is used in a transmitter and a receiver. The BPF limits a bandwidth of the signal in a RF (Radio Frequency) band. The BPF with high precision achieves a precipitous fall of a power level of the out-of-band component. However, the BPF with high precision is expensive.
On the other hand, in the case that an adjacent wireless communication system performs a TDMA (Time Division Multiple Access), even if the BPF has low precision, the interference can be avoided in by sharing a time slot with the adjacent wireless communication system.
One of the technique to share the time slot with the adjacent wireless communication system is disclosed in JP-A 2007-214819(KOKAI). In this reference, the transmitter of a CR (Cognitive Radio) system transmits the signal in the time slot which is used by the adjacent wireless communication system. The transmitter of the CR system transmits the signal with low power in order to avoid giving the interference to adjacent wireless communication system. However, a transmission range is short because of the low power.